The effect of retrovenous, hypothermic, diastolic myocardial perfusion (RVDP) (myocardial oxygen supply) combined with ventricular unloading (myocardial oxygen demand) will be studied in sheep subject to coronary artery ligation. Percent salvage of injured myocardium at risk and prevention of necrosis as assessed by radiolabelled microspheres, Microfil and Tetrazolium staining techniques is hypothesized to be greater in injured hearts supported by combined retrovenous diastolic perfusion and left ventricular bypass. Utilizing zero delay after coronary ligation, the optimum effect on myocardial salvage and function as measured by pressure-dimension analysis for treatment study groups of retrovenous diastolic perfusion and left ventricular bypass will be determined. Closet chest, catheter retrovenous diastolic perfusion (myocardial O2 supply) and intraaortic balloon pumping (IABP) (O2 demand) will be studied in sheep after four hours of coronary ligation to simulate the clinical situation of myocardial injury. The hypothesis will be tested that closed chest combined RVDP and IABP can be practically applied and salvage significant amounts of ischemic myocardium (combined effect greater than when either RVDP or IABP is utilized separately). Myocardial reperfusion as would occur with myocardial revasularization will also be evaluated in these sheep treated with RVDP and IABP. The verification of significant salvage or prevention of injured myocardium in sheep with closed chest combined RVDP and IABP could provide a new clinical therapy for acute coronary occlusion and treatment prior to emergency myocardial revascularization. Similarly RVDP could be utilized in certain patients undergoing cardiac diagnostic or therapeutic (percutaneous transluminal coronary angioplasty, enzymatic thrombolysis) procedures to ensure myocardial perfusion.